Andrzej Boguslawski

A new approach to sub-grid surface tension for LES of two-phase flows

In two-phase flow, the presence of inter-phasal surface - the interface - causes additional terms to appear in LES formulation. Those terms were ignored in contemporary works, for the lack of model and because the authors expected them to be of negligible influence. However, it has been recently shown by a priori DNS simulations that the negligibility assumption can be challenged. In the present work, a model for one of the sub-grid two-phase specific terms is proposed, using deconvolution of the velocity field and advection of the interface using that field. Using the model, the term can be included into LES. A brief presentation of the model is followed by numerical tests that assess the models performance by comparison with a priori DNS results.

Quality of LES Predictions of Isothermal and Hot Round Jet

The paper presents results of LES computations performed for isothermal and non-isothermal variable density jets using high order numerical code. According to the experimental data and linear stability theory the range of the density ratios between jet and the ambient fluids considered in this work encloses the regimes of absolute and convective type of instability. Much attention is paid to the quality of the solutions depending on the mesh resolution and turbulence intensity imposed at the inlet velocity profile. The differences between the solutions obtained using different (advective/conservative) form of the Navier–Stokes equations are also mentioned.

Self-sustained oscillations in a homogeneous-density round jet

The paper is devoted to a new phenomenon of self-sustained oscillations triggered in a round free homogeneous-density jet. It was shown by the experimental investigations supported by the numerical approach based on extensive-Large Eddy Simulations studies that such a self-sustained regime can be established in a homogeneous-density jet, provided that the boundary layer at the nozzle exit is sufficiently thin and the perturbation level sufficiently low. The growth rate of the naturally amplified unstable modes is high enough to induce backflow leading to self-excited oscillations.

Numerical simulation of free jets

Purpose The purpose of the paper is to summarize recent achievements and suggest further research directions in numerical studies of round free jets with particular attention on the influence of the inlet parameters (mean velocity, turbulence intensity, length and time scales) on the jet dynamics. Design/methodology/approach The large eddy simulation (LES) and direct numerical simulation (DNS) are regarded as accurate tools which can support expensive and requiring sophisticated measurements techniques experimental studies. In the paper, the authors present challenges and recent findings related to the LES and DNS of jet type flows in isothermal, heated, excited and reactive conditions. Findings LES of the isothermal jet allowed to identify the new jet instability mechanism leading to the self-sustained oscillations and to determine conditions required to trigger this phenomenon. Numerical simulation on the low-density round jet captured the phenomenon of absolute instability with a very good agreement with the experimental findings. LES/DNS of excited jet exhibited bifurcating and blooming jet and showed that the jet can be directly controlled by excitation frequency what is crucial issue also for flame shape control. Originality/value The paper shows complexity of seemingly simple jet type flow and proves that despite a huge interest in these flows and relatively deep knowledge on the jet dynamics there are still some open issues requiring further studies.

Large eddy simulation predictions of absolutely unstable round hot jet

The paper presents a novel view on the absolute instability phenomenon in heated variable density round jets. As known from literature the global instability mechanism in low density jets is released when the density ratio is lower than a certain critical value. The existence of the global modes was confirmed by an experimental evidence in both hot and air-helium jets. However, some differences in both globally unstable flows were observed concerning, among others, a level of the critical density ratio. The research is performed using the Large Eddy Simulation (LES) method with a high-order numerical code. An analysis of the LES results revealed that the inlet conditions for the velocity and density distributions at the nozzle exit influence significantly the critical density ratio and the global mode frequency. Two inlet velocity profiles were analyzed, i.e., the hyperbolic tangent and the Blasius profiles. It was shown that using the Blasius velocity profile and the uniform density distribution led to a...

Impact of numerical method on a side jets formation in a round jet

Numerical analysis of a formation of side jets in an externally modulated round jet is presented. The research is performed applying Large Eddy Simulation method and high-order codes based on Cartesian and cylindrical coordinates. The main attention is paid to an impact of numerical approach on the formation of the side jets, their number and localisation. The results obtained suggest that on Cartesian meshes the number and directions of the side jets are dependent on the distribution of the mesh nodes.

Comparison of the High-Order Compact Difference and Discontinuous Galerkin Methods in Computations of the Incompressible Flow

High-order compact difference scheme (CD) based on the half-staggered mesh is compared with discontinuous Galerkin method in computations of the incompressible flow. Assessment of the accuracy is performed based on the classical test cases: Taylor–Green vortices, Burggraf flow and also for temporally evolving shear layer. The CD method method provides very accurate results with expected order of accuracy, 4th and 6th. Similarly for the discontinuous Galerkin method provided that the number of degrees of fredom is close to the number of nodes in computations with CD method. Furthermore, it appeared that CD method is much more efficient than the discontinuous Galerkin method of comparable accuracy.

Numerical Predictions of Absolutely Unstable Round Hot Jet

Absolute instability of round low-density jets was studied with spatio-temporal linear stability theory by Monkewitz and Sohn (Monkewitz and Sohn AIAA J, 26(8), 911–916, 1988) [10] and later by Jendoubi and Strykowski (Jendoubi and Strykowski, Phys Fluids 6, 3000, 1994) [5]). They showed, using Briggs (Briggs, Electron-Stream Interaction with Plasmas. Research Monograph, vol 29, The MIT Press, 1964) [2] and Bers (Bers, Physique des Plasmas, 1975) [1] criterion, that in parallel axi-symmetric low-density jet an absolutely unstable mode growing exponentially at the location of its generation can be triggered.

Hybrid MPI/Open-MP acceleration approach for high-order schemes for CFD

The paper presents a hybrid MPI +OpenMP (Message Passing Interface/Open Multi-Processor) algorithm used for parallel programs based on the high-order compact method. The main tools used to implement parallelism in computations are OpenMP and MPI which differ in terms of memory on which they are based. OpenMP works on shared-memory and the MPI on distributed-memory whereas the hybrid model is based on a combination of those methods. The tests performed and described in this paper present significant advantages provided by a combination of the MPI/OpenMP approach. The test computations needed for verifying possibilities of MPI, Open-MP and Hybrid of both tools were carried out using an academic high-order SAILOR solver. The obtained results seem to be very promising to accelerate simulations of fluid flows as well as for application using high order methods.

LES and RANS of pulverized coal oxy-combustion in swirl burners

C fluid transport in the subsurface is important for secondary oil recovery, geothermal heat mining and proppant placement in fractured reservoirs. Limiting fluid loss through fractures in the formation is important for preventing bypassing of oil rich zones. For unconventional gas, larger fractures need to be selectively propped. The process of orthokinetic agglomeration, whereby particles are aggregated by means of fluid shear, has the potential to selectively narrow or block large fractures. This is achieved by coupling the fracture wall shear rate to the fracture size, where higher shear rates in larger fractures result in higher rates of orthokinetic agglomeration. We estimate the differences in shear rate between fracture sizes and perform laboratory investigations on shear-induced particle growth using commercial well mud particulates. Particle growth rates peak at a shear rate of 275s-1. This maximum shows that it is possible to selectively grow particles based on shear. We also show that the availability of precipitating ions act as “glue” maintaining newly formed agglomerates, suggesting the importance of solution chemistry in the process.I adsorptive separation processes have been largely employed for separations in the petrochemical industry. Conventional fixed bed adsorption desorptionseparationis a batch process. As opposed to conventional adsorptive separations, continuous adsorptive separation processes, presents advantages in terms of productivity. Simulated Moving Bed (SMB) technology is a highly selective adsorption desorption process of continuous separation which is often employed in the separation of complex mixtures.This technology has been applied over four decades in the petrochemical industry and currently enjoying preparative an production scale separation of sugars, proteins, pharmaceuticals, fine chemicals, flavorings, foods and enantiomers. This work focuses on mathematical modeling and simulation of SMB systems to be used for xylene isomers separation, which is extensively used in petrochemical industries. Production of polyester fibers and polyethylene terephthalate are the main examples. The operation methodology of SMB is highly complex in nature. Therefore, generally, a model-based control scheme is used so as to obtain a stable operation and better understood SMB process. A great deal of theoretical work has been carried out for developing useful simulation procedures for design and process development purposes. There are several models to be used for adsorptive separations whether it is at the analytical scale or at the preparative/ production scale. The ideal model, the equilibrium dispersive model, the transport dispersive model and the general rate (GR) model, which may be also called non-equilibrium model, are the main examples. The GR model is widely acknowledged as being the most comprehensive among such models available in the literature as it accounts for axial dispersion and all the mass transfer resistances, e.g., external mass transfer of solute molecules from bulk phase to the external surface of the adsorbent, diffusion of the solute molecules through the particle, and adsorption-desorption processes on the site of the particles. The solution of the GR model based SMB governing equations involves the employment of advanced numerical techniques. The solution algorithm usually employs linear adsorption isotherm conditions. This is largely due to the highly complex nature of the resulting equations whennon-linear adsorption isotherms integrated into SMB modeling studies. Ozdural et al. proposed a new algorithm for the numerical solution of non-equilibrium packed-bed adsorption with non-linear adsorption isotherms. Contrary to the generally employed practices, this methodology is not governed by the solution of coupled partial differential equations.The number of partial differential equations to be solved reduces to one. In the present study this technique is extended to SMB systems and applied to Langmuir type nonlinear adsorption isotherm model for xylenes. The solution of the present model predicts the concentration profiles of the components along the columns. For separation of xylenes in petrochemical industry, the present non-equilibrium modelling of SMB under non-linear adsorption isotherms allows a strong perspective and facilitates scale-up procedures.Foamability and foam stability are of main concerns in foam displacement for enhanced oil recovery. This work presents the output of systematic laboratory screening of foam ability and foam Stability of several surfactants. The surfactants examined were Brij 700, Triton X-100, Triton X-405, Zonyl FSO, Hitenol H-10, Hitenol H-20, Noigen N-10 and Noigen N-20. Solution salinity and oil presence effects were explored. Foam was generated by sparging Carbon Dioxide gas at a fixed flow rate through surfactants solutions and R5 parameter as suggested by Lunkenheimera and Malysa (2003) were used for foam stability testing. The results indicate the foam ability of all surfactants except for Triton X-405. Zonyl FSO and Hitenol H-10 were superior in term of foam stability with more stability as surfactants concentration increases. Equivalent optimum foam volumes were obtained for both surfactants but at higher concentrations of Hitenol H-10. Increasing solution salinity from 4% to 10% affected the foam stability negatively for low concentration solutions of Zonyl FSO but had no effect on foam stability of Hitenol H-10 solutions. Foam stability and oil displacement efficiency were tested with different concentrations of Zonyl FSO and Hitenol H-10 solutions at 4% salinity. The presence of oil at the volume fraction implemented, affect the stability of the foam columns. The effect depends on the surfactant-type and surfactants concentrations where stability decreases at low Zonyl FSO concentration range and at all concentrations range tested of Hitenol H-10. In case of Zonyl FSO observations indicate that oil stayed in the lamellas skeleton and plateau boarders with no drain out. To the contrary, Hitenol H-10 was able to lift good portion of the oil column but oil was drained out of the foam structure within a short period of time. Volume 1 • Issue 2 • 2019 Copyright